Propeller protractor



g 1939- J. Y. LICHTENWALNER PROPELLER PROTRACTOR Filed April 9, 1938 INVENTOR.

.]:4Y Y L/CHTEN WALNER A TTOR NE Y.

Patented Aug. 29, 1939 UNITED STATES PATENT OFFICE PROPELLER PROTRACTOR Application April 9,1938, Serial No. 201,144

8 Claims. (Cl. 33-174) This invention relates to means for measuring the pitch angle of the propeller blades of airplanes, and has for its principal object a special protractor adapted to facilitate measuring the pitch angle of the blades in relation to the axis of the propeller or engine shaft when the'plane is at rest or grounded, without dismounting the propeller from the airplane, and regardless of the angle which the fuselage and engine assume when the plane is parked.

Another object of the invention is to provide such an instrument which is self-supporting While in use on the propeller so as to leave the mechanics hands free to make necessary adjustments to the blade.

Specific features and advantages of the invention will appear in the following description and accompanying drawing.

In the drawing:

Figure 1 is a perspective view of one form of my special propeller protractor hung in position on the blade of an airplane propeller.

Figure 2 is a broken side view of the forward end of an airplane engine showing the edge of the base plate of my special protractor aligned thereagainst.

Figure 3 is a broken perspective view showing the dowelled inner end of the blade aligning arm of the device.

Figure 4 is a cross section of Figure 1 as seen from the line 4-4 thereof.

Figure 5 is a plan view of several of the clamping screws used on the instrument- Figure 6 is a front view of the base plate and protractor elements of a modified form of the instrument. 7

Figure l is a vertical cross section of Figured as. seen from the line l-l thereof.

Before describing the invention in' detail, it may be stated that early airplane propellers and hubs were made usually as an integral structure. Later the hubs andblades were constructed separately and secured together, with adjustable blades. Among the present propellersare the controllable and automatic pitch changing types.

To check the pitch or blade angles. of the propeller, usual practice has been to remove the propeller from the engine and put it on a level table and read the blade angles by means of an ordinary protractor. With the great increase in size, weight, and height from the ground of the propellers, it has been found desirable to provide a means for checking the blade angles without removing the propellers from the engine, or even leveling the airplane longitudinally, and this is what my invention accomplishes.

In detailed construction, and considering the form of the invention shown in Figures 1 to 5 inclusive, the instrument comprises a rectangular base plate I provided with a detachable arm 2 projecting at right angles from its face adjacent one edge and provided with a bubble glass 3 and a hook 4 at the outer end of the arm cooperating with a similar hook 5 extending from the upper 10 inner corner of the plate for suspending the instrument from the upper edge 6 of a horizontally disposed airplane propeller blade 'I (here shown as with its outer end broken off to come within the drawing sheet), while on the forward side or 15 face of the base plate l are mounted the protractor elements 8 and 9.

Element 8 is aprotractor disk or dial revolvably mounted on a suitable hub projecting from the plate and retained by a disk ill. The dial is 20 suitably graduated in degrees of are over the required'operating portion of its margin as in dicated at H, and provided with gear teeth l2 along the remaining portion, engaged by a pinion I3 operated by a thumb wheel M in the known 25 manner to revolve the dial to any desired point and hold it by friction of the parts. The arcuate scale may be any desired length.

Element 9 is an arcuate plate fitting close to the dial 8 and graduated as at l5 with a Vernier scale to cooperate with scale ii of the dial. Plate 9 is formed with an arcuate slot IS in which it is supported by screws or headed studs i! so that it is movable for a limited distance about the dial, and it is provided with gear teeth i8 on its upper edge engaged by a pinion l9 operated by a thumb wheel 20 for arcuate adjustment of the Vernier in the same manner that the dial is operated by the wheel l4.

Securedto the face of the dial 8 is a bubble glass 2! so that the angular displacement of the dial fromv the vertical may be read on the scale. The scale may be of any desired length.

Arm 2 is provided with a foot 22 for positioning it against the base plate and is held in place as by a substantial thumb screw A, which screws into a threaded hole 23 in the base plate, but is additionally located in its position by a couple of dowel pins 24 projecting from its outer surface and which enter locating holes drilled in the base plate.

Hooks 4 and 5 are directed outwardly in planes parallel to that of the base plate and they are respectively provided with flat shanks 26 2'! guided in corresponding sockets 28-, 29 and held in desired vertical adjustment by thumb screws B, C, which pass through any of the several holes 30, 3|, respectively drilled through the shanks of the hooks. By this means the elevation of either or both ends of the instrument may be vertically determined on the propeller blade, so that the arm 2 will be parallel to the longitudinal axis or cen-- ter line X of the blade when in position shown in Figure 1, and hence the base plate will stand vertically across the back of the blade at right angles to said center line. pered to a thinner section toward the outer end, a filler to compensate for this difference must be placed under the outer end of the arm 2, or that is, between the arm and the rear side of the propeller blade so that the arm 2 will be parallel to the center line. This filler is supplied by having the end of thumb screw B project slightly beyond the outer or rear side of the arm as shown in Figure 4 at B".

lfhe size of the required filler will depend on the particular design of the propeller; however, in the use of the instrument for most accurate results, it is presupposed that the user knows the formula or characteristics of the blades he is measuring, and accordingly different lengths of thumb screws are provided as indicated in Figure 5, each suitably marked as A,B,CorDto designate the propeller blade it is to be used with at the end of of the arm. The screws are otherwise interchangeable so that any of them may be used for clamping the foot of the arm and the hook 5 in place, and when the instrument is disassembled for packing, the screws may be screwed in a row of threaded holes provided along the lower margin of the base plate as indicated at A to E.

The pitch of the blade is generally required at a radius point of the 42 inches, though sometimes at 54 inches radius, and it is frequently the practice to have a mark or marks on the blade to designate these points as the central axis is not available as a measuring point, but when the blade is not marked the point for the required pitch measurement may easily be obtained by reference to the particular design data.

Since the curve of the upper or leading edge 6 of the blade also varies with the design, the several holes 33-3l are provided in the shanks of the hooks at predetermined points to insure parallelism of the arm 2 and the center line of the particular design of blade being measured. The various holes are of course suitably marked for the difierent blade designs, though it is manifest without additional showing in the drawing that the shanks could be slotted to provide for any degree of vertical adjustment and marked for various blade designs.

'In using the instrument, it should be understood that most airplane engine housings or crank cases have an exposed surface at some point which extends at right angles to the axis of the shaft such as the surface 32 of the engine 33, and the forward edge l-a of the base plate is pressed against such a surface while arm 2 is maintained in horizontal extension with the aid of bubble glass 3, and dial 8 is revolved until its bubble glass shows level. The instrument is then preferably removed from the engine and arcuate plate 9 is revolved by wheel 20 to bring its pointer in line with the pointer of the dial in its new position. The instrument is next suspended by its hooks from the leading edge of the substantially horizontally projecting blade to be measured for pitch, with the plate I with its rear edge in contact with and extending across the back fiat or As the blades are ta-.

slightly concave side of the propeller blade, in line with 42 inch radius position or any other point desired to be measured. The propeller blade is now carefully moved slightly up or down by hand until the bubble of glass 3 shows its center line to be level. Dial 8 is again revolved by wheel I4 until the bubble of its glass 2| shows level, and a reading of the scale will give the pitch of the blade at the point measured.

If plate 9 were rigidly secured to the base plate two readings would be required instead of one, but the moving of the plate 9 as described compensates for the angular position of the plane on the ground.

If no such flat surface as at 32 is available on the engine assembly, any other surface extending at right angles to the engine axis either within or Without the plane may be used, or any surface extending parallel to the engine axis may be used by applying either the upper or lower edge of rectangular base plate for the first leveling-up operation.

In the modified form of my device shown in Figures 6 and '7 the operation is somewhat simplified. In this form the rectangular base plate is designated 34, the arm 35, here shown in section as L shape, its foot 36, securing screw 31, and protractor elements 38, and 39. Both elements comprise heavy graduated quadrants 40, 4|, pendulously suspended from a common axis 43 so that they are free to swing, and clamping plates 44, 45, with screws 44', 45', to lock them after they have come to rest, and both are provided with bubble glasses 46, 47, but which are merely for checking purposes.

The cross section shown in Figure '7 shows one form of the actual construction, and with the two pendulous members pivotally suspended from a two step shouldered pin 48 so that when either is clamped the other will be free to swing. Any other pivotal or frictionless, or ball bearing mounting may be used if desired, as the figures are only illustrative of one method of carrying out the idea.

To operate this form, one edge of the base plate is placed against the engine or other surface as explained for the other form described, either clamp screw 44' or 45 is released and its pendulum member permitted to swing to vertical position, then reclamped in the new posiclamped in the new position. The included angle I shown between the pointers on the scale is the pitch of the blade.

No limitations are to be implied by the length or proportions of the reading scales shown on the instruments of the drawing, as the scales may be of any desired lengths, depending on the maximum angles desired to be measured.

Having thus described two forms of my invention, and the manner of its use, it will be seen to be capable of variations in the construction of its various features, and any such as come within the spirit of the invention are intended to be included in my appended claims.

I therefore claim:

1. A propeller pitch measuring device comprising a base plate, a protractor pivotally mounted on one side of said base plate, said base plate provided with an edge adapted to extend across a propeller blade in contact therewith, and

means for suspending said base plate in such 75 position from the upper edge of a horizontally extending blade of a mounted propeller and insuring the plane of rotation of the protractor extending at right angles to the longitudinal center line of said blade, said protractor provided with a marginal scale and a leveling glass, and means for rotating the protractor and holding it to any point of adjustment, a Vernier scale adjacent the protractor scale arranged for arcuate movement about the same and provided with means for holding it at any point of ad- Justment.

2. A propeller pitch measuring device comprising a rectangular base plate, a circular protractor with a scale on its margin pivotally mounted on the face of said plate, an arm extending at right angles from the face of said plate and plane of rotation of said protractor, a hook adjaceent the outer end of said arm extending at right angles to the arm, a similar hook extending from the plate arranged to cooperate with the first hook in suspending the device from the edge of a propeller blade with the plate projecting at right angles therefrom.

3. A propeller pitch measuring device comprising a rectangular base plate, a circular protractor with a scale on its margin pivotally mounted on the face of said plate, an arm extending at right angles from the face of said plate and plane of rotation of said protractor, a hook adjacent to the outer end of said arm extending at right angles to the arm, a similar hook extending from the plate arranged to cooperate with the first hook in suspending the device from the edge of a propeller blade with the plate projecting at right angles therefrom, a leveling glass mounted on said arm extending at right angles to the plane of said plate, and a leveling glass mounted on said protractor extending parallel to its plane of rotation.

4. A propeller pitch measuring device comprising a rectangular base plate, a circular protractor with a. scale on its margin pivotally mounted on the face of said plate, an arm extending at right angles from the face of said plate and plane of rotation of said protractor, a hook adjacent the outer end of said arm extending at right angles to the arm, a similar hook extending from the plate arranged to cooperate with the first hook in suspending the device from the edge of a propeller blade with the plate projecting at right angles therefrom, and means for adjusting the distance of the end of the arm from said blade.

5. A propeller pitch measuring device comprising a rectangular base plate, a circular protractor with a scale on its margin pivotally mounted on the face of said plate, an arm extending at right angles from the face of said plate and plane of rotation of said protractor, a hook adjacent to the outer end of said arm extending at right angles to the arm, means for adjusting the height of the hook relative to the arm, a similar hook extending from the plate arranged to cooperate with the first hook in suspending the device from the edge of a propeller blade with the plate projecting at right angles therefrom.

6. A propeller pitch measuring device comprising a base plate provided with edges extending at ninety degrees from one another, an arcuate protractor member pivotally mounted on one side of said plate, an arm extending at right angles from the face of said plate and plane of rotation of said protractor, and means arranged and adapted for suspending said device from a mounted horizontally extending propeller blade with said plate projecting at right angles to said blade and said arm level and aligned with the center line of said blade.

'7. A propeller pitch measuring device comprising a base plate provided with a straight edge for aligning across the propeller blade, an arcuate protractor element with a scale on its margin pendulously suspended on one side of said plate to swing in a plane parallel thereto and provided with means for clamping it against swinging, a second arcuate protractor element with a reading mark on its margin pendulously suspended from the same axis as the previous element mentioned and arranged to swing with its margin close to the margin of said previous element, and means for clamping said second arcuate protractor member against swinging.

8. In a construction as set out in claim 7, a bubble leveling glass secured respectively to each of the protractor elements.

JAY Y. LICH'IENWALNER. 

